Density of the Ocean

"Somewhere, something incredible is waiting to be found." - Carl Sagan

Learn about how temperature and salinity affect the density of water with just a few common household items! With just some food coloring, you will be able to see the different layers of Earth’s ocean, and start understanding the complex system of our ocean.

Ingredients/Tools:

• 2 small transparent container (plastic cups or glass jars)

• 1 medium transparent container

• Cold and warm water

• Salt

• Food coloring (3 different colors)

• An ice cube tray

• A small sponge

• A spoon or eye dropper

Directions:

1. Cold water on top of cold salt water/Cold water on top of cold fresh water

Mix some food coloring into water and fill an ice cube tray. Meanwhile, prepare two cups with the same amount of water. In one cup, mix two tablespoons of salt and add food coloring that is a different color than the ice cubes. In the other cup, mix in another color of food coloring. On the ice freezes, add one cube into each of the two cups at the same time and see what happens to each of the cups. Feel free to make predictions about what will happen!

2. Salt water on top of warm fresh water

In the medium container, mix some food coloring with warm water. In another cup, prepare some cold water with two tablespoons of salt and a different color of food coloring mixed in. Then with your spoon or eye dropper, slowly add in the salt water on top of the warm water, avoiding any splashing or mixing. What happens?

3.Layered ocean

Using the medium container again, we will now add three different types of water, cold fresh water, warm fresh water, and cold salty water. Color each type of water a different color. To make the salty water, again add 2 tablespoons of salt. Make each type of water a different color so that you can clearly see the layers. Add the salt water into the container first. Then, float a sponge on top of the water and carefully add in the warm fresh water. With your spoon or eye dropper, add the final layer of cold fresh water. How many layers can you see? Is there any mixing?

The Science Behind It:

So why did the fresh water float on top of the salt water? Well that’s because salt water has a higher mass to volume ratio due to all the salt particles. This makes the salt water denser than the fresh water. And what about the freshwater? Why did the warmer water float on top of the freshwater? The water molecules in warm water are more active than they are in cold water, so they occupy a greater volume, making warm water less dense than cold water even though they are both fresh.